Post-traumatic stress disorder (PTSD) is characterized by persistent and intrusive memories of traumatic experiences, and general hyper-arousal. Current models of the neural systems involved in PTSD highlight abnormalities in an emotion regulation system involving amygdala hyper-reactivity accompanied by reduced top-down regulation from medial prefrontal regions such as anterior cingulate cortex. However, few previous studies have examined the effects of trauma on functional interactions between the amygdala and medial prefrontal cortex, particularly within the context of engaging and regulating emotional arousal responses. The purpose of the proposed research is to investigate the effects of trauma and PTSD on the brain regions that support and regulate emotional arousal responses to affective stimuli. Environmental factors are uniquely involved in PTSD relative to other psychiatric disorders, as traumatic events serve as a trigger for PTSD, and the intensity and duration of trauma is correlated with symptom severity. In addition, twin studies suggest that heritable factors contribute to vulnerability to the disorder. An additional goal of the proposed research will be to examine gene x environment interaction models of PTSD by focusing on genetic polymorphisms in FKBP5, a gene coding for a co-chaperone in the HPA axis system, as risk alleles have been shown to predict PTSD development after a trauma, and this gene has been studied extensively by our group.